Key contact system for electronic organs



Aug, 26, 1958 J. M. LESTER KEY common: SYSTEM FOR ELECTRONIC ORGANS Filedmarch 2, 1955 2 Sheets-Sheet 1 INVENTOR.

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BY JQH/V ll/l. LESTER Filed March 2, 1955 J. M. LESTER ,848,92@

KEY CONTACT SYSTEM FOR ELECTRONIC ORGANS 2 Sheets-Sheet 2 IN V EN TOR.

BY JOHN M. LESTER Unite tatcs P313111 rimmed Aug. 26, 1958 KEY CONTACT SYSTEM FOR ELECTRONIC ORGANS John M. Lester, Garden City, N. Y.

Application March 2, 1955, Serial No. 491,561

1 Claim. (Cl. 84-127) This invention relates to electronic contacts. More specifically, to contacts for use in electronic instruments, such as, electronic organs, utilizing a conductive rubber member as a mechanical and electrical element.

The primary object of the invention is to provide an improved contact for electronic instruments of the organ type permitting of a simple and inexpensive construction.

Another object of the invention is to provide an instrument contact which eliminates undesirable key clicks.

A further object of the invention is to provide a contact for electrical instruments in which the volume of the tone generated by the contact may be varied by key depression.

A still further object of the invention is to provide electronic instrument contacts in which the rate of attack may be controlled.

A still further object of the invention is to provide a key contact for an electronic instrument which supplied mechanical cushioning upon key depression.

Other objects of the invention will become apparent by reference to the following detailed description taken in connection with the accompanying drawings in which:

Figure 1 is a vertical sectional view of a contact constructed in accordance with the present invention.

Figure 2 is a plan view of the embodiment shown in Figure 1 with the key removed.

Figure 3 is a vertical sectional view of the embodiment shown in Figure 1 in which the key is depressed.

Figure 4 is a horizontal sectional view showing an ultimate embodiment of the invention, and

Figure 5 is a graph illustrating one of the features of the invention.

Figure 6 is a detail of another embodiment of the invention.

Referring now to the drawings wherein like numbers refer to like and corresponding parts throughout the several views. The particular embodiment of the invention disclosed in Figures 1, 2 and 3 comprises, in general, a key member 10 having a flexible portion 8, such as a plastic organ key, which is supported by plastic lock member 11. Attached to the underside and the forward end of key member 10 at point 9 is a cylindrical member 12 which is constructed of conductive material such as conducting rubber tubing. This may be rubber with a finely divided conductor, such as graphite interspersed throughout the rubber mass. Beneath key member 10 is contact plate 15 on which is supported a pair of conductive contacting elements 16 and 17 which are spaced from each other and from contacting member 12. The axis of contacting member 12 is normal to the longitudinal axis of conductors 16 and 17 and the length of the contacting member 12 is sufiicient to bridge the space between the conductors 16 and 17. The conducting members 16 and 17 are electrically connected in a conventional manner to a tone generator in such a manner that upon electrically bridging these conductors 16 and 17, a tone will be generated.

As key member 10 is depressed by the finger of the operator, the contacting member 12 electrically bridges the conductors 16 and 17 at the instant it contacts these members. This bridging of conductors 16 and 17 permits the creating of a tone in the normal manner. However, since contacting member 12 is constructed of a pliable substance, such as conducting rubber, further depression of key member 10 permits the contacting member '12 to assume an oval shape such as shown in Figure 3. Since the impedance between conductors 16 and 17 is controlled by the unit impedance of contacting member 12 and the area of this member 12 which bridges conductors 16 and 17, increased depression of key member 10 decreases the impedance between conductors 16 and 17. As a result, the amplitude of the tone generated by depression of key 10 may be increased by further depression until the contacting member 12 assumes a flattened shape. As a result, the operator is not only able to create a tone associated with a particular key 10, but is further able to increase the volume of the tone generated by additional pressure on key 10. Further, since the volume of the tone generated may be inversely proportional to the impedance of the bridge eliminated by the conductors 16 and 17, the rate of attack may be controlled by the operator in accordance with the rate of depression of the key itself.

Since the contacting member itself is of a resilient material, not only does it permit actual electrical contacting or closing of the circuit at the tone generated, but its resiliency provides a cushioning effect as the key is depressed.

In the embodiment of the invention disclosed in Figures 1, 2, and 3, it is readily recognized that an approximately linear relationship is established between the depression of key 10 and the bridge resistance or impedance between conductors 16 and 17. In particular embodiments it may be desired to have the impedance decreased more rapidly than linearly with depression of key 10. To achieve such a result the embodiment shown in Figure 4 is utilized. In this embodiment, conductor 16, supported by plate 15 terminates in a pair of wedge shaped members 20 and 21 having their points directed towards each other on opposite sides of center line 25. In like manner, conductor 17 is terminated in a pair of wedge shaped plates 22 and 23 which are supported in a base plate 15 in symmetrical fashion to plates 20 and 21 on opposite sides of center line 25. The center line 25 is mechanically aligned with the axis of contacting member 12. In this embodiment, as key 10 is depressed, contacting member 12 bridges between conductors 16 and 17, creating the tone as in the previous embodiment. However, further depression of key 10 not only causes the contacting member 12 to be compressed and assume an oval shape, but due to the positions of contacting switches 21, 22, and 23, the bridging impedance between conductors 16 and 17 decreases at a much faster rate with depression of key 10. As a result of this configuration, the intensity of the tone produced increases at a predetermined rate with linear depression of key 10. Figure 5 discloses how the amplitude of the tone generated, signified by curve 50, increases with depression of key 10. The envelope of this curve 51 is a representation of the resulting amplitude. It may be seen that by proper design of the conductors this envelope may be made to have any desired curve.

In an embodiment of this invention constructed by the inventor, a conducting rubber member which gives a change of impedance from 100,000 ohms at contact depression to 5,000 ohms upon full depression of the key. The change of impedance in this particular change gives a somewhat exponential curve to the volume of the tone produced with key depression. This produces a pleasing 3 organ effect as the tone builds to maximum amplitude.

The material for the contacting member may have a very low or a very high impedance depending upon the amount and density of the conductive material used in the construction of the pliable material. It is readily seen that while the cross section shown for the contacting member is circular in the open position, other shapes may be used with equal convenience.

It is readily seen that the key contacting construction disclosed lends itself readily for use in printed circuit techniques. The conductors 16 and 17 in the embodiment shown are metal strips on a base plate 15 and may be plated elements, such as copper or silver supported by a nonconducting base plate such as a plastic material. It is further recognized that while the embodiment shown discloses a single-pole, single-throw type of switch, other switching combinations can, of course, be obtained by utilizing the principle of the present invention.

Although two modifications of the simple embodiment of the present invention are disclosed and described in detail, it is quite obvious to one skilled in the art that many changes may be made in the size, shape, arrangement and details of the elements of the structure and the proportioning thereof without departing from the spirit and scope as defined by the appending claim.

Figure 6 shows another embodiment of the invention for obtaining non-linear response. This is obtained by selectively painting coats of conducting rubber cement on the tubing member 10. The layers of paint or rubber cement in the manner shown in Figure 6 wherein the first coat 60 is put on about one-half of the surface of the tube. The next coat 61, 61' is placed on each side of the bottom, but not at the point of contact on the bottom. The third coat 62, 62 is further spaced as is the fourth coat 63, 63. For purposes of illustration these conductive coats are shown much thicker than they might be in practice. Therefore, when the key is depressed, the impedance will decrease in a non-linear manner proportionate to the amount of pressure.

I claim:

A key switch for use in an electronic musical instrument comprising a movably plastic key member, a pair of conductive members below said member and forming part of a tone generating circuit, a tubular, flexible, conductive member attached to said key and having selective bridging contact with said conductive members to close said circuit, the flexibility of said tubular member providing a variable impedance between said conductive members.

References Cited in the file of this patent UNITED STATES PATENTS 1,778,374 Spielmann Oct. 14, 1930 1,849,724 Pudelko Mar. 15, 1932 1,899,884 Severy Feb. 28, 1937 2,260,412 Stephens Oct. 28, 1941 2,303,516 Mehren Dec. 1, 1942 2,470,148 Demuth May 17, 1949 2,510,608 Stephen June 6, 1950 2,528,086 Schenck Oct. 31, 1950 2,694,128 Maurin Nov. 9, 1954 

